Compatibility Check and Requirements Update

• Documentation: Update the requirements.txt to point to the latest versions.
• Library: Verify if the library is compatible with Qt 6.7.

v1.2.2: Clarify and simplify copyright and LGPL license

- Update the copyright header in all source files with a simplified version that uses the SPDX license identifier for the LGPL.
- Combining the two copyright holders into a single line.
- Add the `COPYRIGHT.md` file that clarify who’s holding the copyright and the special propietary use exception for one copyright holder.
- Adding the GPL license along with the LGPL addendum.
- No functional changes were made to the source code.

v1.2.1: Fixing an issue with key paths in parser

- The previous fix for the key paths uncovered an issue in the parser that was caused by an mixed migration. This is fixed now, by using the `Value::valueFromKey()` method, instead of `Value::value()`.
- Introduced the method `Value::hasKey()` that allows testing for keys that contain dots.
- Fixed API comments.
- Adding tests to the `Value::begin()` and `Value::end()` method, only return valid iterators for arrays.
- Moving implementations from header to source files.

v1.2.0: Enhancing and extending the library.

- API Change: renaming `parseFile` into `parseFileOrThrow` (and similar) to match the library standard. Existing `parseFile` will not throw exceptions. See documentation.
- Completing initial documentation.
- Adding missing API documentation.
- Adding missing interfaces in the `Value` class.
- Make maintenance script compatible with Windows.

v1.1.0: Update `README.md`

- Update the `README.md` to point to the new documentation page.

v1.0.1: Last minute fixes

- Update the include headers with the correct version of the script.
- Fixing the CMakeLists.txt file that contained a typo.
- Adding the include path to the CMake file.